For this purpose, moulds are known comprising a punch having a lower end portion which penetrates into the cavity of a lowerly positioned die to define, in combination with this latter, a cavity for forming the container headpiece; the punch possesses a cylindrical outer surface arranged to exactly engage the tubular body of the container, the lower end of which is positioned adjacent to the edge of the forming cavity and penetrates through the cylindrical surface of the die as an exact fit, to couple the punch to the die.
The container headpiece is formed within the forming cavity and is hot-bonded under pressure to the lower end of the tubular body, typically by making the punch and die approach each other axially after inserting a plastic blank into the forming cavity; alternatively, this can be done by injecting fluidized plastic into the forming cavity while in the static configuration.
In this manner a tubular container is produced composed of the tubular body and the headpiece, which usually possesses a threaded mouth through which the container contents are extracted.
The mouth of the forming cavity is closed by the lower end portion of the cylindrical surface of the punch, which penetrates axially as an exact fit, together with the lower end of the tubular body, within the cylindrical concave surface of the die. As the pressure in the forming cavity is very high during the forming process, said mutually engaging cylindrical surfaces of the punch and die (with the tubular body interposed) must mate with very little gap therebetween, in particular to prevent upward seepage of the plastic material, which would result in undesirable filament-like protuberances projecting into the container chamber.
Because of this, the insertion of the punch into the die during the mutual axial approach stage is a delicate and critical operation which consequently requires a relatively lengthy time and particular care; moreover the risk of said undesirable filament-like protuberances forming cannot be eliminated in practice.
The applicant is aware of a mould for forming the top of deformable tubular plastic containers comprising a tubular body and a headpiece of plastic material bonded to one end of the tubular body.
The mould comprises a punch having an outer surface arranged to engage the container tubular body as an exact fit, and an end portion projecting axially from the lower end of the cylindrical outer surface).
A die is arranged to form, in combination with the lower surface of the punch, a cavity (F) for forming the headpiece of the container.
Said die has a concave surface arranged to receive as an exact fit, by axial penetration, the lower end of the cylindrical outer surface of the punch together with the lower end of the tubular body of the container.
The headpiece is formed within the forming cavity (F) and is pressure-bonded therein to the lower end of the tubular body by a radial deformation means of the punch, positioned on its outer surface and extending annularly along the entire circumference of this surface to act on the tubular body of the container, said means being arranged to assume a normal position in which its outer surface does not project radially from the cylindrical outer surface of the punch, and an active position in which it is urged in a radial direction in such a manner as to press the tubular body (51) against the opposing surface of the die.
The above features are partially disclosed by EP-A-0810073, but are not suitable to overcome the above said drawbacks.
An object of this invention is to provide a mould able to overcome said drawbacks.